The present invention relates to a device for the discrimination between two values "1" and "0" of a signal using direct current (DC) offset compensation. The device of the present invention is used, for example, as a device for discriminating between two values of a signal in an LSI optical data link. The two values "1" and "0" of a signal in an LSI optical data link correspond to the "light is ON" state and the "light is OFF" state, respectively.
When the signal which is sent from a transmitting side and is discriminated at a receiving side, if it is impossible to obtain the central level at the receiving side by DC regeneration, a method for discriminating between the two values "1" and "0" of the received signal is carried out as illustrated in FIGS. 1(A), 1(B) and 1(C). From a received signal SIGNAL-I, the inverted signal SIGNAL-II and the shifted signal SIGNAL-III are obtained as illustrated in FIGS. 1(A) and 1(B). The amount of the shift is equal to the amplitude v.sub.s of SIGNAL-I. Comparing the two signals SIGNAL-II and SIGNAL-III, a signal SIGNAL-IV is obtained so as to represent the result of the discrimination of the received signal SIGNAL-I as illustrated in FIG. 1(C).
In this method, however, a problem is incurred if the basic levels of SIGNAL-I and SIGNAL-II do not coincide and hence a DC offset OFS is formed between SIGNAL-I and SIGNAL-II as illustrated in FIGS. 1(D) and 1(G), under a condition that the value of maximum amplitudes of SIGNAL-I and SIGNAL-II is limited within a predetermined value v(max). This is because, the discrimination margin MG formed by SIGNAL-II and SIGNAL-III is reduced as compared with the case of FIGS. 1(A), 1(B) and 1(C) as illustrated in FIGS. 1(E) and 1(H), and accordingly the discrimination of the values of the received signal cannot always be conducted correctly.
Also, a prior art method is disclosed in U.S. Pat. No. 4,027,152 in which a signal which is sent from a transmitting side and which has three values is used and the discrimination of the signal received at a receiving side is carried out by using a basic level which is obtained as the result of the integration of the received signal. However, this prior art method requires a process of making the three valued signal and causes a reduction for the discrimination margin because of the use of the three valued signal. Therefore, this prior art cannot provide a complete solution for the discrimination of the received signal having plural values.